Preparation of calcium carbide



United States Patent PREPARATION OF CALCIUM CARBIDE Sieds Koopal, Sittard, and Joannes H. C. lyloison, Simpelveld, Netherlands, assignors to Stamicarbon N. V., Heerlen, Netherlands No Drawing. Application December 28, 1953, Serial No. 400,770,

Claims priority, application Netherlands December 30, 1952 2 Claims. (Cl. 23-208) The invention relates to a process for the production of calcium carbide in a shaft furnace.

The starting material used in this manufacture of calcium carbide consists of a mixture of a solid fuel, mainly composed of carbon, such as coke, charcoal and anthracite, and unslaked lime or a calcareous material (limestone or dolomite). which, by heating can be converted into calcium oxide, the amount of heat and the high temperature required for the formation of the carbide being produced by burning part of the fuel with an oxygen-containing blast. In this process hereinafter referred to as the shaft-furnace process the continuous feeding of the mixture of fuel and starting material, as well as the withdrawal of the inflammable gas produced, takes place through the top of the furnace, while a liquid carbide-containing melt is formed in the lower part of the furnace in the so-called melt pot from which it can be discharged through a tap hole. The blast is introduced at an intermediate level.

Should it be desired for example to manufacture a carbide which on being decomposed with water will yield 200 litres of acetylene per kg., a mixture of coke'and limestone consisting of 100 parts by weight of coke and 50 parts by weight of limestone, may be used with a blast having a dew point of 69 C. and composed of 70% by volume of technical oxygen and 30% by vol ume of steam. It has not been found feasible to start the process without taking special measures, partly because of the fact that the furnace gets clogged up with lime.

Even-if the amount of limestone is considerably reduced at first and after that gradually increased again, very great difficulties are experienced. This is also the case when an oxygen-nitrogen mixture is used for the blast or when carbides other than calcium carbide have to be prepared.

OBI ECTS It is an object of the present invention to prepare calcium carbide in shaft furnaces by an improved method of starting the process. It is a further object to prepare calcium carbide in a shaft furnace in such a way that in the beginning of the process the furnace does not get clogged up with unreacted calcareous material.

A further object of this invention is to obtain a more fluid melt during the start of the process than that obtained in prior art methods of forming calcium carbide in a shaft furnace. Another object of the invention is to preheat the lower part of the furnace before the carbide is collected therein as a molten slag. Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter.

It should be understood, however, that the detailed description and specific example, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modificacations within the spirit and scope of the invention will 2,749,219 Patented June 5, 1956 become apparent from this detailed description to those skilled in the art.

GENERAL DESCRIPTION According to the present invention these objects are accomplished in the following manner.

Surprisingly it has been found that difiiculties at the start of the process can be entirely obviated, if the furnace is started in the same way as a normal slagging producer used for the preparation of producer gas or oxygas, where the ash is consequently withdrawn in the form of a liquid-slag, and only after said process has got going properly, for instance after some hours a start is made with the carbide manufacture by first adding the calcium compound needed for the carbide preparation to the charge, and by subsequently increasing the oxygen content of the blast.

According to the present invention, in the production of carbide from a mixture of solid carbonaceous fuel and the calcareous compound to be converted into carbide by the shaft furnace process as hereinbefore defined, the step is included of starting the process by employing only sufiicient of the calcareous compound as will form a liquid slag in a normal coal gasifying process, and when said slag has been formed properly for some hours the proportions of the calcareous compound and solid fuel in the starting mixture charged, are adjusted to those required for forming carbide and the oxygen content of the blast is then raised to the proportion required for carbide production. I The oxygen content of the blast is preferably increase at the moment when the modified charge reaches the burner zone. The best results are obtained if the oxygen content of the blast is first raised to a percentage higher than which is ultimately needed for the manufacture of carbide of a desired quality, and after that gradually reduced to the value required. This reduction of the oxygen percentage to the final value is completed in a period of 624 hours, depending on the composition of the carbide melt which, instead of being discharged once in l-3 hours as is done in the normal producer process, is now tapped oif every half hour for example.

When an oxygen-steam mixture is used for the blast, the generator may consequently be started in the same manner as a slagging producer; when using a blast of oxygen-enriched air the generator is likewise started as a normal slagging producer used for the preparation of producer gas.

EXAMPLES A more complete understanding of this invention and the operation thereof may be had by reference to the following examples.

Example I For the preparation of carbide capable of yielding about 210 litres of acetylene per kg., in which an oxygen-steam mixture is used for the blast, the shaft furnace is started in the same way as a normal slagging producer used for)the manufacture of oxygas (oxygen blown producer gas The charge supplied was a mixture of parts by weight of coke and 6-8 parts by weight of limestone. The amount of limestone used in this process is dependent on the amount and the composition of the ash in the coal. The blast used was a mixture of steam and oxygen with a dew point of 84 C. (composition of the mixture: 45% by volume of technical oxygen, the remainder consisting of steam).

Under these conditions the temperature in the burner zone amounts to 1800-2000. The slag obtained is very fluid and may be discharged for example every two hours.

3 Instead of lime Martin slag may also be used to good advantage.

The first step in changing over to the carbide process is the addition of a charge consisting of 100 parts by weight of coke and 50 parts by weight of limestone.

At about the time when said charge reaches the burner level, the dew point of the blast is lowered to 65 C. (oxygen content 75% by volume). This causes the temperature in the furnace to rise rapidly. Now the melt is regularly withdrawn every half hour and its CaCzcontent determined. The CaCz-content rises gradually. After the CaCz-content of the melt has attained a value which corresponds with 100.1itres of acetylene per kg., the dew point is gradually raised until the process has approximately stabilized. .This is achieved in a period of about 12 hours. The product thus obtained has a carbide content of 59.8%, which corresponds with 210 litres of acetylene per kg. of carbide.

Example I] For the purpose of preparing carbide using oxygenenriched air, a shaft furnace is started in the same manner as a normal slagging producer used'for the preparation of producer gas. The charge con 1st ofamixture The liquid slag is tapped off every, two zhours'.- fAfter the process has balanced out, w-hich-take s -a-few hours, the charge is changed into a mixture a- -1m" arts b weight of coke and parts by weight of liheestbfi At about the same time that the charge reaches the burner level, the oxygen content of the blast is raised to 55% by volume, after which the slag formed is tapped off every half hour. The carbide content of the melt starts to rise gradually. By slowly lowering the oxygen percentage, the process is kept in hand so that after 18 hours, and with the blast having an oxygen content of 50% by volume, the process has been stabilized. The carbide obtained under these conditions is capable of yielding 200:1itres of acetylene per kg.

4 CONCLUSION The present invention provides a method of starting the manufacture of carbides in a shaft furnace, whereby difficulties, such as clogging up of the shaft by unreacted material, or a badly running carbide-containing slag are avoided.

By applying the method according to the invention, it is possible to start the process in any easy way, whereby the temperature of the furnace is raised little by little and whereby continuously a molten slag with a slowly increasing carbide content is produced, which always can be easily tapped off.

We claim:

1. A process for producing a calcium carbide containing slag which comprises charging a shaft furnace with a mixture of solid carbonaceous fuel and calcareous ma: terial containing 6 to 8 parts by weight of calcareous material per 100 parts fuel, contacting said mixture with an oxygen-containing blast consisting essentially of 55% steam and oxygen, by volume, at a temperature of 18002000 C., permitting gas formed thereby to escape from the top of said furnace and withdrawing liquid slag from the bottom thereof, thereafter increasing the content of calcareous material in the mixture charged to said furnace so that said mixture comprises 35 to parts calcareous compound per 100 parts fuel, then increasing the oxygen content of said blast to 75% by volume,

' and continuing the escape of gas and withdrawal of slag containing calcium carbide of increasing content from said furnace.

2. The process of claim 1 wherein the oxygen content of said blast is decreased to stabilize said process after carbide content in the slag removed from said furnace reaches the desired point.

References Cited in the file of this'patent UNITED STATES PATENTS 826,743 Price July 24, 1906 1,098,534 Servais June 2, 19-14 1,146,766 Wallmann July 13, 1915 2,174,900 .Snyder Oct. 3, 1939 2,380,008 Abrams et a1 July 10, 1945 2,476,760 Ohlsson July 19, 1949 

1. A PROCESS FOR PRODUCING A CALCIUM CARBIDE CONTAINING SLAG WHICH COMPRISES CHARGING A SHAFT FURNACE WITH A MIXTURE OF SOLID CARBONACEOUS FUEL AND CALCAREOUS MATERIAL CONTAINING 6 TO 8 PARTS BY WEIGHT OF CALCAREOUS MATERIAL PER 100 PARTS FUEL, CONTACTING SAID MIXTURE WITH AN OXYGEN-CONTAINING BLAST CONSISTING ESSENTIALLY OF 55% STEAM AND 45% OXYGEN, BY VOLUME, AT A TEMPERATURE OF 1800-2000* C., PERMITTING GAS FORMED THEREBY TO ESCAPE FROM THE TOP OF SAID FURNACE AND WITHDRAWING LIQUID SLAG FROM THE BOTTOM THEREOF, THEREAFTER INCREASING THE CONTENT OF CALCAREOUS MATERIAL IN THE MIXTURE CHARGED TO SAID FURNACE SO THAT SAID MIXTURE COMPRISES 35 TO 50 PARTS CALCAREOUS COMPOUND PER 100 PARTS FUEL, THEN INCREASING THE OXYGEN CONTENT OF SAID BLAST TO 55-75% BY VOLUME, AND CONTINUING THE ESCAPE OF GAS AND WITHDRAWAL OF SLAG CONTAINING CALCIUM CARBIDE OF INCREASING CONTENT FROM SAID FURNACE. 